During assembly of an aircraft, fastening operations are performed synchronously on opposite sides of various structures. A fastening operation may include drilling, countersinking and fastener insertion on one side of a structure, and terminating the end of each inserted fastener on the opposite side of the structure.
Consider fastening operations on a wing box of an aircraft. Drilling, countersinking and fastener insertion are performed by a robotic system outside the wing box. Sleeve and nut placement are performed inside the wing box by manual labor. A person enters a wing box through a small access port, and performs the sleeve and nut placement with hand tools while lying flat inside the wing box. On the order of several hundred thousand fasteners are installed and terminated on common aircraft wings.
It would be highly desirable to eliminate the manual labor and fully automate the fastening operations on both sides of the wing box. However, while placing a nut over the threads of a bolt might be a simple task for a human, it is not so simple for a robot. Precise positioning and orientation of a nut over a bolt is a complex task.
This task becomes even more complex due to space constraints inside the wing box. The wing box forms a narrow space that, at the tip, is only several inches high (see FIG. 4 for an example of a wing box). Moreover, the narrow space is accessible only through an access port. The robot would have to enter the narrow space via the access port, navigate past stringers inside the narrow space, locate ends of inserted fasteners, and position an end effector and place a sleeve and nut over each fastener end.
The task becomes even more complex because aircraft tolerances are extremely tight. The task becomes even more complex because the end effector typically weighs 40 to 50 pounds. The task becomes even more complex because the robot inside the narrow space has to synchronize its tasks with those of a robot outside the wing box.